New Isotope Methods for Estimating Milk Intake and Yield

Two isotope tracer methods, based on the transfer of isotopic tracer via milk from a female to offspring, were developed for estimating milk intake of nursing offspring. One method depended upon the transfer of tritiated water from female to offspring in milk and simultaneous determination of water turnover of the offspring by deuterium oxide. The second method was based on the transfer of radiocesium from female to offspring in milk and required the use of whole body counting techniques for evaluating the radiocesium body burden of the offspring. Experiments evaluating the two methods were with hand-reared Holstein calves given fixed milk intake. The methods gave valid estimates of milk intake; estimates were within±2.5% of the actual intakes. The application and limitations of these methods for estimating milk intake and yield of other species are discussed.